Method for forming isolation with multi-step structure

ABSTRACT

A method for forming a semiconductor device structure is provided. The method includes forming first and second well regions with different conductivity types in a semiconductor substrate. A well interface is formed between the first and second well regions. The method also includes patterning the semiconductor substrate to form a first fin structure in the first well region, a second fin structure in the second well region, and a first trench between the first and second fin structures. The first trench exposes the well interface in the semiconductor substrate. The method further includes forming insulating spacers on opposite sidewalls of the first trench and etching the semiconductor substrate below the first trench using the insulating spacers as an etch mask, to form a second trench below the first trench. In addition, the method includes filling the first and second trenches with an insulating material.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a Divisional of pending U.S. patent application Ser. No. 16/211,949, filed Dec. 6, 2018, which claims the benefit of U.S. Provisional Application No. 62/738,305, filed on Sep. 28, 2018, the entirety of which is incorporated by reference herein.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation.

As the semiconductor industry has progressed into nanometer technology process nodes in pursuit of higher device density, higher performance, and lower costs, challenges from both fabrication and design issues have resulted in the development of three-dimensional designs, such as the fin field effect transistor (FinFET). FinFETs are fabricated with a thin vertical “fin” (or fin structure) extending from a substrate. The advantages of a FinFET include a reduction of the short-channel effect and a higher current flow.

Although existing FinFET manufacturing processes have generally been adequate for their intended purposes, they have not been entirely satisfactory in all respects, especially as device scaling-down continues. For example, well leakage (which can cause latch-up) becomes increasingly important as the fin structure and the shallow trench isolation (STI) are shrunk. It is a challenge to form reliable FinFET device at smaller and smaller sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It should be noted that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1A to 1I illustrate perspective views of various stages of manufacturing a semiconductor device structure in accordance with some embodiments.

FIGS. 2A to 2I illustrate cross-sectional representations of various stages of manufacturing a semiconductor device structure in accordance with some embodiments.

FIGS. 3A to 3D illustrate cross-sectional representations of various stages of manufacturing a semiconductor device structure in accordance with some embodiments.

FIGS. 4A to 4D illustrate cross-sectional representations of various stages of manufacturing a semiconductor device structure in accordance with some embodiments.

FIGS. 5A to 5D illustrate cross-sectional representations of various stages of manufacturing a semiconductor device structure in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the subject matter provided. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Furthermore, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. It should be understood that additional operations can be provided before, during, and after the method, and some of the operations described can be replaced or eliminated for other embodiments of the method.

Embodiments for manufacturing semiconductor device structures are provided. The semiconductor device structures may include a semiconductor substrate having a first well region and a second well region that have different conductivity types and are adjacent to each other. A first fin structure and a second fin structure are respectively formed in the first well region and the second well region. The first fin structure and the second fin structure protrude from the semiconductor substrate and are adjacent to each other. Afterwards, a multi-step isolation structure is formed between the first fin structure and the second fin structure. The multi-step isolation structure includes a first isolation portion corresponding to the upper portions of the first fin structure and the second fin structure, and a second isolation portion extending from the bottom surface of the first isolation portion. The second isolation portion has a top width that is narrower than the bottom width of the first isolation portion, so that the fin structures on opposite sides of the multi-step isolation structure have a reverse T-like shape.

FIGS. 1A to 1I illustrate perspective views of various stages of manufacturing a semiconductor device structure 10 a and FIGS. 2A to 2I illustrate cross-sectional representations of various stages of manufacturing the semiconductor device structure 10 a in accordance with some embodiments. In addition, FIGS. 2A to 2I illustrate the cross-sectional representations of the semiconductor device structure shown along line A-A′ in FIGS. 1A to 1I in accordance with some embodiments. In some embodiments, the semiconductor device structure is implemented as a fin field effect transistor (FinFET) structure. As shown in FIGS. 1A and 2A, a substrate 100 is provided. In some embodiments, the substrate 100 is a semiconductor substrate, such as a bulk semiconductor, a semiconductor-on-insulator (SOI) substrate, or the like, which may be doped (e.g. with a P-type or an N-type dopant) and/or undoped. In some embodiments, the substrate 100 is a wafer, such as a silicon wafer. Generally, an SOI substrate includes a layer of a semiconductor material formed on an insulator layer. The insulator layer may be, for example, a buried oxide (BOX) layer, a silicon oxide layer, or the like. The insulator layer is provided on a substrate, typically a silicon or glass substrate.

Other substrates, such as a multi-layered or gradient substrate may also be used. In some embodiments, the semiconductor material of the substrate 100 includes silicon; germanium; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or a combination thereof. In some embodiments, the substrate 100 includes silicon. In some embodiments, the substrate 100 includes an epitaxial layer. For example, the substrate 100 has an epitaxial layer overlying a bulk semiconductor.

In some embodiments, the substrate 100 includes a PMOS region for P-type FinFETs formed thereon. The PMOS region of the substrate 100 may include Si, SiGe, SiGeB, or an III-V group semiconductor material (such as InSb, GaSb, or InGaSb). In some embodiments, the substrate 100 includes an NMOS region for N-type FinFETs formed thereon. The NMOS region of the substrate 100 may include Si, SiP, SiC, SiPC, or an III-V group semiconductor material (such as InP, GaAs, AlAs, InAs, InAlAs, or InGaAs).

In some other embodiments, the substrate 100 includes one or more PMOS regions and one or more N MOS regions. For example, the substrate 100 may include well regions 100 a-100 c adjacent to each other. The well region 100 b may have a first conductivity type (e.g., N-type) and be formed between and adjacent to the well region 100 a and the well region 100 c that have a second conductivity type (e.g., P-type), so that a well interface 101 a is formed between the well region 100 a and the well region 100 b, and a well interface 101 b is formed between the well region 100 c and the well region 100 b. In those cases, the well region 100 b serves as the NMOS region and the well region 100 b serve as the PMOS region. In some other embodiments, the substrate 100 includes an undoped region 100 d formed on the well regions 100 a-100 c. The undoped region 100 d may be used as channel regions for FinFETs formed on the substrate 100.

Afterwards, a mask structure is formed over the substrate 100 in accordance with some embodiments. More specifically, a first masking layer 102 and a second masking layer 104 of the mask structure are successively stacked over the substrate 100 for the subsequent patterning process. In some embodiments, the first masking layer 102 may be used as an etch stop layer when the second masking layer 104 is patterned. The first masking layer 102 may also be used as an adhesion layer that is formed between the undoped region 100 d of the substrate 100 and the second masking layer 104.

In some embodiments, the first masking layer 102 is made of silicon oxide and is formed by a deposition process, such as a chemical vapor deposition (CVD) process, a low-pressure chemical vapor deposition (LPCVD) process, a plasma enhanced chemical vapor deposition (PECVD) process, a high-density plasma chemical vapor deposition (HDPCVD) process, a spin-on process, or another applicable process.

In some embodiments, the second masking layer 104 is made of silicon oxide, silicon nitride, silicon oxynitride, or another applicable material. In some other embodiments, more than one second masking layer 104 is formed over the first masking layer 102. In some embodiments, the second masking layer 104 is formed by a deposition process, such as a chemical vapor deposition (CVD) process, a low-pressure chemical vapor deposition (LPCVD) process, a plasma enhanced chemical vapor deposition (PECVD) process, a high-density plasma chemical vapor deposition (HDPCVD) process, a spin-on process, or another applicable process.

After formation of the first masking layer 102 and the second masking layer 104 of the mask structure, a patterned photoresist layer 106 may be formed over the second masking layer 104 for subsequent definition of one or more fin structures in the substrate 100. In some embodiments, the patterned photoresist layer 106 is formed by a photolithography process. The photolithography process may include photoresist coating (e.g., spin-on coating), soft baking, mask aligning, exposure, post-exposure baking, developing the photoresist, rinsing and drying (e.g., hard baking).

The first masking layer 102 and the second masking layer 104 of the mask structure are patterned by using the patterned photoresist layer 106 as an etch mask, as shown in FIGS. 1B and 2B in accordance with some embodiments. After the first masking layer 102 and the overlying second masking layer 104 are etched, a patterned first masking layer 102 and a patterned second masking layer 104 are formed, so that portions of the undoped region 100 d of the substrate 100 are exposed.

After the portions of the undoped region 100 d of the substrate 100 are exposed by forming the patterned first masking layer 102 and the patterned second masking layer 104, the patterned photoresist layer 106 is removed, in accordance with some embodiments. Afterwards, the substrate 100 is patterned by one or more etching processes using the patterned first masking layer 102 and the patterned second masking layer 104 as an etch mask, as shown in FIGS. 1C and 2C in accordance with some embodiments.

More specifically, the exposed portions of the undoped region 100 d of the substrate 100 are removed, and the well regions 100 a-100 c below the exposed portions of the undoped region 100 d of the substrate 100 are partially removed by an etching process using the patterned second masking layer 104 and the patterned first masking layer 102 as an etch mask. As a result, fin structures and trenches in the substrate 100 are formed. In order to simplify the diagram, fin structures 110 a-110 f protruding from the substrate 100 and trenches 112 a-112 e are depicted as an example. In some embodiments, each of the fin structures 110 a-110 f has a width that gradually increases from the top portion to the bottom portion, so that each of the fin structures 110 a-110 f has a tapered fin width and sidewall. In some embodiments, each of the trenches 112 a-112 e has substantially the same width (e.g., the width W1 shown in FIG. 2C).

In some embodiments, the fin structure 110 a and the fin structure 110 b are defined in the well region 100 a by forming the trench 112 a in the well region 100 a between the fin structure 110 a and the fin structure 110 b. The fin structure 110 c and the fin structure 110 d are defined in the well region 100 b by forming the trench 112 c in the well region 100 b between the fin structure 110 c and the fin structure 110 d. The fin structure 110 e and the fin structure 110 f are defined in the well region 100 c by forming the trench 112 e in the well region 100 c between the fin structure 110 e and the fin structure 110 f.

In addition, the trench 112 b is formed between the fin structure 110 b and the fin structure 110 c and directly above the interface 110 a between the well region 100 a and the well region 100 b, so that the interface 110 a is exposed from the trench 112 b. Similarly, the trench 112 d is formed between the fin structure 110 d and the fin structure 110 e and directly above the interface 110 b between the well region 100 b and the well region 100 c, so that the interface 110 b is exposed from the trench 112 d.

In some embodiments, the etching process for formation of fin structures 110 a-110 f is a dry etching process or a wet etching process. For example, the substrate 100 is etched by a dry etching process, such as a reactive ion etching (RIE), neutral beam etching (NBE), the like, or a combination thereof. The etching process may be a time-controlled process, and continue until the fin structures 110 a-110 f are formed and reach a predetermined height. A person of ordinary skill in the art will readily understand other methods of forming the fin structures, which are contemplated within the scope of some embodiments.

After the fin structures 110 a-110 f are formed, an insulating layer 120 is formed over the substrate 100 to conformally cover the sidewalls and the top surfaces of the fin structures 110 a-100 f, and the bottom of the trenches 112 a-112 e, as shown in FIGS. 1D and 2D in accordance with some embodiments. In some embodiments, the insulating layer 120 is made of silicon oxide, silicon nitride, silicon oxynitride, silicon carbide (SiC), fluorosilicate glass (FSG), a low-k dielectric material, or another suitable dielectric material. The insulating layer 120 may be deposited by a chemical vapor deposition (CVD) process, a flowable CVD (FCVD) process, a spin-on-glass process, or another applicable process.

Afterwards, an insulating layer 120 is formed over the substrate 100 to cover the fin structures 110, as shown in FIG. 1D in accordance with some embodiments. In some embodiments, the insulating layer 120 is made of silicon oxide, fluorosilicate glass (FSG), a low-k dielectric material, and/or another suitable dielectric material or another low-k dielectric material. The insulating layer 120 may be deposited by a chemical vapor deposition (CVD) process, a flowable CVD (FCVD) process, an atomic layer deposition (ALD) process, or another applicable process.

After the insulating layer 120 is formed, the insulating layer 120 is etched to form insulating spacers 120 a over the substrate 100, as shown in FIGS. 1E and 2E in accordance with some embodiments. In some embodiments, the insulating layer 120 is anisotropic etched using, for example, a dry etching process, so as to remove the insulating layer 120 on the top surfaces of the fin structures 110 a-110 f and the bottom of the trenches 112 a-112 e. As a result, the insulating spacers 120 a are formed on opposite sidewalls of each of the trenches 112 a-112 e, so that portions of the well regions 110 a-110 c including the well interfaces 101 a and 101 b are exposed through the trenches 112 a-112 e. In some embodiments, each of the trenches 112 a-112 e having insulating spacers 120 a formed therein has substantially the same width (e.g., the width W2 shown in FIG. 2E) that is less than the width W1 shown in FIG. 2C.

After the insulating spacers 120 a are formed, trenches 114 a-114 e are formed in the well regions 100 a-100 c of the substrate 100 and respectively below the trenches 112 a-112 e, as shown in FIGS. 1F and 2F in accordance with some embodiments. In some embodiments, the exposed portions of the well regions 110 a-110 c below the trenches 112 a-112 e are etched by an anisotropic etching process using the insulating spacers 120 a as an etch mask. For example, the well regions 110 a-110 c of the substrate 100 are etched by a dry etching process, such as a reactive ion etching (RIE), neutral beam etching (NBE), the like, or a combination thereof.

After the anisotropic etching process, the trenches 114 a-114 e with tilted sidewalls 115 are respectively extended from the bottom surface of the trenches 112 a-112 e into the well regions of substrate 100, so that each of the trenches 114 a-114 e has a top width W3 that is substantially equal to the width W2 shown in FIG. 2E and less than the width W1 shown in FIG. 2C. As shown in FIGS. 1F and 2F, the trench 114 b is formed between the well region 100 a and the well region 110 b and directly above the interface 110 a in accordance with some embodiments, so that the interface 110 a is exposed from the trench 114 b. Similarly, the trench 114 d is formed between the well region 100 b and the well region 100 c and directly above the interface 110 b in accordance with some embodiments, so that the interface 110 b is exposed from the trench 114 d.

After the trenches 114 a-114 e are formed, an insulating material 130 is formed over the substrate 100 to cover the patterned second masking layers 104 over fin structures 110 a-110 f and fill the trenches 114 a-114 e and the trenches 112 a-112 e, as shown in FIGS. 1G and 2G in accordance with some embodiments. In some embodiments, the insulating material 130 is made of silicon oxide, fluorosilicate glass (FSG), a low-k dielectric material, and/or another suitable dielectric material or another low-k dielectric material. The insulating material 130 may be deposited by a chemical vapor deposition (CVD) process, a flowable CVD (FCVD) process, a spin-on-glass process, or another applicable process.

In some embodiments, the insulating spacers 120 a are removed from the opposite sidewalls of the trenches 112 a-112 e prior to the formation of the insulating material 130, as shown in FIGS. 1G and 2G. In some other embodiments, the insulating spacers 120 a are remained in the trenches 112 a-112 e during the formation of the insulating material 130. In those cases, the insulating spacer 120 a may be made of a material that is the same as or similar to the insulating material 130.

Afterwards, the insulating material 130 is recessed to expose the top surface of the patterned second masking layer 104, in accordance with some embodiments. For example, the insulating material 130 over the top surface of the patterned second masking layer 104 is etched back or removed by a chemical mechanical polishing (CMP) process. After the top surface of the patterned second masking layer 104 is exposed, the patterned second masking layer 104 and the patterned first masking layer 102 are removed by one or more etching processes, so as to expose the top surfaces of the fin structures 110 a-110 f. For example, the patterned second masking layer 104 and the patterned first masking layer 102 are removed by a dry etching process, a wet etching process, or a combination thereof.

Afterwards, the insulating material 130 is further recessed to form an isolation feature over the substrate 100 and surrounding the fin structures 110 a-110 f, as shown in FIGS. 1H and 2H in accordance with some embodiments. In some embodiments, the insulating material 130 is recessed by an etching process (such as a dry etching process or a wet etching process, or a combination thereof), so that the top surface of the isolation feature is substantially level with the interfaces between the undoped region 100 d and the well regions 100 a-100 c.

In some embodiments, the isolation feature made of the remaining insulating material 130 includes multi-step isolation structures 134. More specifically, each of the multi-step isolation structures 134 is formed between the corresponding two adjacent fin structures formed over the substrate 100. The multi-step isolation structure 134 includes a first isolation portion 131 (which may also be referred to an upper isolation portion) and a second isolation portion 133 (which may also be referred to a lower isolation portion). The first isolation portion 131 is formed in the corresponding trench (such as the trenches 112 a-112 f indicated in FIG. 2F) to correspond to the upper portions of the fin structures 110 a-110 f. The second isolation portion 133 is formed in the corresponding trench (such as the trenches 114 a-114 f indicated in FIG. 2F) to extend from the bottom surface of the first isolation portion 131 and to correspond to the lower portions of the fin structures 110 a-110 f. As a result, the second isolation portion 133 between the fin structure 110 b and the fin structure 110 c is formed directly above the well interface 101 a. Also, the second isolation portion 133 between the fin structure 110 d and the fin structure 110 c is formed directly above the well interface 101 b.

In some embodiments, the second isolation portion 133 has tilted sidewalls 135 and a top width (which is substantially equal to the top width W3 of the trenches 114 a-114 e shown in FIG. 2F) that is narrower than the bottom width of the first isolation portion 131 (which is substantially equal to the width W1 shown in FIG. 2C). Therefore, the first isolation portion 131 has a bottom area that is greater than the top area of the second isolation portion 133. As a result, the multi-step isolation structures 134 have a T-like shape and each of the fin structures 110 a-110 f has a reverse T-like shape corresponding to the T-like shape of the multi-step isolation structure 134.

The isolation feature that includes multi-step isolation structures 134 prevents electrical interference or crosstalk. A portion of each of the fin structures 110 a-110 f is embedded in and surrounded by the isolation feature. Compared to the use of a shallow trench isolation (STI) structure for prevention of electrical interference or crosstalk, the use of the multi-step isolation structure 134 can increase the isolation depth between the well regions (e.g., between the well region 100 a and the well region 100 b, or between the well region 100 b and the well region 100 c), thereby increasing the well leakage path. As a result, the latch-up phenomenon can be improved or prevented. Compared to the use of a deep trench isolation (DTI) structure for prevention of electrical interference or crosstalk, the use of the multistep isolation structure 134 reduces the loss of the volume of the well regions 100 a-100 c near the well interfaces 101 a and 101 b. As a result, it can prevent the resistance of the well regions 100 a-100 c from being increased, and therefore the device's performance can be maintained or improved. In addition, the fin structures 110 a-110 f with the reverse T-like shape provide good mechanical strength, and therefore the fin collapse can be prevented. As a result, the yield of the semiconductor device can be increased.

After the isolation feature including the multi-step isolation structures 134 are formed, source/drain features 140 are formed in the fin structures 110 a-110 f, and a gate structure 151 is formed across the fin structures 110 a-110 f, so as to form the semiconductor device structure 10 a, as shown in FIGS. 1I and 2I in accordance with some embodiments. In some embodiments, a dummy gate structure (not shown) is formed across the fin structures 110 a-110 f and over the isolation feature including the multi-step isolation structures 134 before the formation of the source/drain features 140 and the gate structure 151.

In some embodiments, the dummy gate structure includes a dummy gate dielectric layer and a dummy gate electrode layer formed over the dummy gate dielectric layer. The dummy gate dielectric layer and the dummy gate electrode layer may be made of silicon oxide and polysilicon, respectively. Afterwards, gate spacers 136 are formed on the opposite sidewalls of the dummy gate structure in accordance with some embodiments. The gate spacer 136 may be made of low-K dielectric materials, silicon nitride, silicon oxide, silicon oxynitride, silicon carbide, or another applicable dielectric material.

After formation of the gate spacers 136, the source/drain features 140 are formed in the fin structures 110 a-110 f laterally adjacent to and exposed from the dummy gate structure, in accordance with some embodiments. In some embodiments, the source/drain structures 140 are formed by recessing the portions of the fin structures 110 a-110 f laterally adjacent to the dummy gate structure and growing semiconductor materials in the formed recesses in the fin structures 110 a-110 f by performing epitaxial (epi) growth processes.

After the source/drain features 140 are formed, an insulating layer 142 is formed over the fin structures 110 a-110 f and covers the isolation feature and the source/drain features 140, as shown in FIG. 1I in accordance with some embodiments. The insulating layer 142 may serve as an interlayer dielectric (ILD) layer and may be a single layer or include multiple dielectric layers with the same or different dielectric materials. For example, the insulating layer 142 may be a single layer made of silicon oxide, tetraethyl orthosilicate (TEOS), phosphosilicate glass (PSG), borosilicate glass (BSG), boron-doped phosphosilicate Glass (BPSG), fluorosilicate glass (FSG), undoped silicate glass (USG), or the like. The insulating layer 142 may be deposited using any suitable method, such as a chemical vapor deposition (CVD) process, a plasma enhanced CVD (PECVD) process, flowable CVD (FCVD) process, the like, or a combination thereof.

Afterwards, the dummy gate structure is removed and replaced by the gate structure 151, as shown in FIGS. 1I and 2I in accordance with some embodiments. In some embodiments, the gate structure 151 includes a gate dielectric layer 146, a gate electrode layer 148, and the gate spacers 136. The gate dielectric layer 146 may be made of metal oxides, metal nitrides, metal silicates, transition metal-oxides, transition metal-nitrides, transition metal-silicates, oxynitrides of metals, or other applicable dielectric materials. The gate electrode layer 148 may be made of a conductive material, such as aluminum, copper, tungsten, titanium, tantalum, or another applicable material. The gate structure may further include a work functional metal layer (not shown) between the gate dielectric layer 146 and the gate electrode layer 148, so that the gate structure has the proper work function values. The work function metal layer may be made of TiN, TaN, Ru, Mo, Al, WN, ZrSi₂, MoSi₂, TaSi₂, NiSi₂, WN, or a combination thereof. Alternatively, the work function metal layer may be made of Ti, Ag, TaAl, TaAlC, TiAlN, TaC, TaCN, TaSiN, Mn, Zr, or a combination thereof.

Many variations and/or modifications can be made to embodiments of the disclosure. FIGS. 3A to 3D illustrate cross-sectional representations of various stages of manufacturing a semiconductor device structure 10 b in accordance with some embodiments. The semiconductor device structure 10 b shown in FIG. 3D is similar to the semiconductor device structure 10 a shown in FIG. 2I. In some embodiments, the materials, formation methods, and/or benefits of the semiconductor device structure 10 a shown in FIGS. 2A to 2I may also be applied in the embodiments illustrated in FIGS. 3A to 3D, and therefore may not be repeated.

In some embodiments, a structure as shown in FIG. 2E is provided. Afterwards, the exposed portions of the well regions 110 a-110 c below the trenches 112 a-112 e are etched using the insulating spacers 120 a as an etch mask. Unlike the anisotropic etching process shown in FIG. 2F, the well regions 110 a-110 c of the substrate 100 are etched by an isotropic etching process, such as a wet etching process. After the isotropic etching process, each of the trenches 114 a′-114 e′ has convex sidewalls 115′. Similar to the trenches 114 a-114 e shown in FIG. 2F, each of the trenches 114 a′-114 e′ has a top width W3 that is substantially equal to the width W2 shown in FIG. 2E and less than the width W1 shown in FIG. 2C.

After the trenches 114 a-114 e′ are formed, an insulating material 130 is formed over the substrate 100 by a method that is the same as or similar to that shown in FIG. 2G, so as to cover the patterned second masking layers 104 over fin structures 110 a-110 f and fill the trenches 114 a′-114 e′ and the trenches 112 a-112 e, as shown in FIG. 3B in accordance with some embodiments. In some embodiments, the insulating spacers 120 a are removed from the opposite sidewalls of the trenches 112 a-112 e prior to the formation of the insulating material 130, as shown in FIG. 3B. In some other embodiments, the insulating spacers 120 a are remained in the trenches 112 a′-112 e′ during the formation of the insulating material 130.

Afterwards, the insulating material 130 is recessed by a method that is the same as or similar to that shown in FIG. 2H, so as to form an isolation feature over the substrate 100 and surrounding the fin structures 110 a-110 f, as shown in FIG. 3C in accordance with some embodiments. In some embodiments, the isolation feature made of the remaining insulating material 130 includes multi-step isolation structures 134′. Unlike the multi-step isolation structures 134 shown in FIG. 2H, the multi-step isolation structure 134′ includes a first isolation portion 131 and a second isolation portion 133′ (which may also be referred to a lower isolation portion). The second isolation portion 133′ has convex sidewalls 135′ and a top width W3 (which is substantially equal to the top width W2 of the trenches 114 a′-114 e′ shown in FIG. 3A) that is narrower than the bottom width of the first isolation portion 131 (which is substantially equal to the width W1 shown in FIG. 3A). Therefore, the first isolation portion 131 has a bottom area that is greater than the top area of the second isolation portion 133′. As a result, the multi-step isolation structures 134′ have a T-like shape and each of the fin structures 110 a-110 f has a reverse T-like shape corresponding to the T-like shape of the multi-step isolation structure 134′.

Similar to the multi-step isolation structure 134 shown in FIG. 2H, the multi-step isolation structure 134′ also can increase the well leakage path and reducing the loss of the volume of the well regions 100 a-100 c near the well interfaces 101 a and 101 b. Moreover, the fin structures 110 a-110 f with the reverse T-like shape provide good mechanical strength. In addition, the second isolation portion 133′ with convex sidewalls 135′ in the multi-step isolation structure 134′ can prevent the reduction of the well leakage path when the well junctions (i.e., the well interfaces 101 a and 101 b) shifts in the formation of the well regions 110 a-110 c.

After the isolation feature including the multi-step isolation structures 134′ is formed, a gate structure 151 is formed across the fin structures 110 a-110 f by a method that is the same as or similar to that shown in FIG. 2I, so as to form the semiconductor device structure 10 b, as shown in FIG. 3D in accordance with some embodiments.

Many variations and/or modifications can be made to embodiments of the disclosure. FIGS. 4A to 4D illustrate cross-sectional representations of various stages of manufacturing a semiconductor device structure 10 a′ in accordance with some embodiments. The semiconductor device structure 10 a′ shown in FIG. 4D is similar to the semiconductor device structure 10 a shown in FIG. 2I. In some embodiments, the materials, formation methods, and/or benefits of the semiconductor device structure 10 a shown in FIGS. 2A to 2I may also be applied in the embodiments illustrated in FIGS. 4A to 4D, and therefore may not be repeated.

In some embodiments, a structure as shown in FIG. 2D is provided. Afterwards, such a structure is covered by a patterned photoresist layer 125, as shown in FIG. 4A in accordance with some embodiments. In some embodiments, the patterned photoresist layer 125 includes trench openings 125 a and 125 b to respectively expose the trench 112 b and the trench 112 d which are covered by the insulating layer 120 and located respectively and directly above the well interface 101 a and the well interface 101 b.

The insulating layer 120 exposed from the trench openings 125 a and 125 b is etched by a method that is the same as or similar to that shown in FIG. 2E, so as to form insulating spacers 120 a on opposite sidewalls of the trench 112 b and the trench 112 d and expose portions of the well regions 110 a-110 c including the well interfaces 101 a and 101 b under the trench 112 b and the trench 112 d, in accordance with some embodiments.

Afterwards, the exposed portions of the well regions 110 a-110 c under the trench 112 b and the trench 112 d are etched by a method that is the same as or similar to that shown in FIG. 2F, so as to respectively form the trench 114 b and the trench 114 d below the trench 112 b and the trench 112 d, as shown in FIG. 4B.

In some embodiments, the patterned photoresist layer 125 is removed after trench 114 b and the trench 114 d are formed. Afterwards, an isolation feature is formed over the substrate 100, as shown in FIG. 4C in accordance with some embodiments. In some embodiments, the isolation feature includes isolation structures 137 and multi-step isolation structures 134. More specifically, each of the isolation structures 137 includes a first isolation portion 131, and each of the multi-step isolation structures 134 includes a first isolation portion 131 and a second isolation portion 133 that has tilted sidewalls 135. In some embodiments, the isolation structures 137 are formed in the trench 112 a, the trench 112 c, and the trench 112 e. Moreover, the multi-step isolation structures 134 are formed in the trenches 112 b and 114 b and the trenches 112 d and 114 d. As a result, the isolation structures 137 have a bottom surface that is substantially level with the bottom surface of the first isolation portion 131 of the multi-step isolation structures 134. The isolation structures 137 and the multi-step isolation structures 134 are formed by methods that are the same as or similar to those shown in FIGS. 2G and 2H, in accordance with some embodiments.

After the isolation feature including the isolation structures 137 and the multi-step isolation structures 134′ is formed, a gate structure 151 is formed across the fin structures 110 a-110 f by a method that is the same as or similar to that shown in FIG. 2I, so as to form the semiconductor device structure 10 a′, as shown in FIG. 4D in accordance with some embodiments.

Many variations and/or modifications can be made to embodiments of the disclosure. FIGS. 5A to 5D illustrate cross-sectional representations of various stages of manufacturing a semiconductor device structure 10 b′ in accordance with some embodiments. The semiconductor device structure 10 b′ shown in FIG. 5D is similar to the semiconductor device structure 10 b shown in FIG. 3D and the semiconductor device structure 10 a′ shown in FIG. 4D. In some embodiments, the materials, formation methods, and/or benefits of the semiconductor device structure 10 b shown in FIGS. 3A to 3D and the semiconductor device structure 10 a′ shown in FIGS. 4A to 4D may also be applied in the embodiments illustrated in FIGS. 5A to 5D, and therefore may not be repeated.

In some embodiments, a structure as shown in FIG. 4A is provided. Afterwards, the insulating layer 120 exposed from the trench openings 125 a and 125 b are etched by a method that is the same as or similar to that shown in FIG. 4B, so as to form insulating spacers 120 a on opposite sidewalls of the trench 112 b and the trench 112 d and expose portions of the well regions 110 a-110 c including the well interfaces 101 a and 101 b under the trench 112 b and the trench 112 d, as shown in FIG. 5A in accordance with some embodiments.

After the insulating spacers 120 a are formed, the exposed portions of the well regions 110 a-110 c under the trench 112 b and the trench 112 d are etched by a method that is the same as or similar to that shown in FIG. 3A, so as to respectively form the trench 114 b′ and the trench 114 d′ below the trench 112 b and the trench 112 d, as shown in FIG. 5B.

In some embodiments, the patterned photoresist layer 125 is removed after trench 114 b′ and the trench 114 d′ are formed. Afterwards, an isolation feature is formed over the substrate 100, as shown in FIG. 5C in accordance with some embodiments. In some embodiments, the isolation feature includes isolation structures 137 and multi-step isolation structures 134′. In some embodiments, similar to the semiconductor device structure 10 a′ shown in FIG. 4D, each of the isolation structures 137 includes a first isolation portion 131, and the isolation structures 137 are formed in the trench 112 a, the trench 112 c, and the trench 112 e. In some embodiments, similar to the semiconductor device structure 10 b shown in FIG. 3D, each of the multi-step isolation structures 134′ includes a first isolation portion 131 and a second isolation portion 133′ that has convex sidewalls 135′, and the multi-step isolation structures 134 are formed in the trenches 112 b and 114 b and the trenches 112 d and 114 d. As a result, the isolation structures 137 have a bottom surface that is substantially level with the bottom surface of the first isolation portion 131 of the multi-step isolation structures 134′. The isolation structures 137 and the multi-step isolation structures 134′ are formed by methods that are the same as or similar to those shown in FIGS. 3B and 3C, in accordance with some embodiments.

After the isolation feature including the isolation structures 137 and the multi-step isolation structures 134′ is formed, a gate structure 151 is formed across the fin structures 110 a-110 f by a method that is the same as or similar to that shown in FIG. 3D, so as to form the semiconductor device structure 10 a′, as shown in FIG. 5D in accordance with some embodiments.

Embodiments of semiconductor device structures and methods for forming the same are provided. The formation of the semiconductor device structure includes forming a first fin structure over a semiconductor substrate and in a first well region of first conductivity type in the semiconductor substrate, and a second fin structure over the semiconductor substrate and in the second well region of an opposite second conductivity type in the semiconductor substrate. Afterwards, a multi-step isolation structure is formed between the first fin structure and the second fin structure. The multi-step isolation structure includes a first isolation portion and a second isolation portion extending from a bottom surface of the first isolation portion. The second isolation portion has a top width that is narrower than the bottom width of the first isolation portion. In the multi-step isolation structure, since the isolation depth increases between the adjacent well regions, leakage (which may cause latch-up) between the adjacent well regions can be reduced. Since the lower portion (i.e., the second isolation portion) of the multi-step isolation structure has a top width that is narrower than the bottom width of the upper portion (i.e., the first isolation portion) of the multi-step isolation structure first isolation feature, the fins can have a reverse T-like shape. As a result, the mechanical strength of the fin structures can be increased, thereby preventing fin collapse, and therefore the yield of the semiconductor device can be improved. In addition, compared to one-step deep trench isolation technology for latch-up prevention, the loss of the well volume can be mitigated by the use of the multi-step isolation structure. As a result, it can prevent the resistance of the well region from being increased, and therefore the device's performance can be maintained or improved.

In some embodiments, a method for forming a semiconductor device structure is provided. The method includes forming a first well region and a second well region in a semiconductor substrate. The first well region and the second well region have different conductivity types, and a well interface is formed between the first well region and the second well region. The method also includes patterning the semiconductor substrate to form a first fin structure in the first well region, a second fin structure in the second well region, and a first trench between the first fin structure and the second fin structure. The first trench exposes the well interface in the semiconductor substrate. The method further includes forming insulating spacers on opposite sidewalls of the first trench and etching the semiconductor substrate below the first trench using the insulating spacers as an etch mask, to form a second trench below the first trench. In addition, the method includes filling the first trench and the second trench with an insulating material.

In some embodiments, a method for forming a semiconductor device structure is provided. The method includes forming an undoped region, a first well region, and a second well region in a semiconductor substrate. The first well region and the second well region are below the undoped region and adjacent to each other. The method also includes patterning the doping region, the first well region and the second well region to form a plurality of fin structures protruding from the semiconductor substrate and forming two insulating spacers on two opposite sidewalls of each of the plurality of fin structures. The insulating spacers expose a portion of the first well region and a portion of the second well region. The method further includes etching the exposed portion of the first well region and the exposed portion of the second well region to form a plurality of trenches in the semiconductor substrate, removing the insulating spacers above the plurality of trenches, and correspondingly forming a plurality of isolation features in the plurality of trenches after the removal of the insulating spacers.

In some embodiments, a method for forming a semiconductor device structure is provided. The method includes forming a first well region and a second well region in a semiconductor substrate. A well interface is formed between the first well region and the second well region. The method also includes forming a first fin structure in the first well region, a second fin structure in the second well region, and a third fin structure in the first well region and between the first fin structure and the second fin structure by a first etching process, so that a first trench is formed between the first fin structure and the third fin structure and a second trench is formed between the third fin structure and the second fin structure. The second trench is directly above the well interface. The method further includes forming insulating spacers on opposite sidewalls of the second trench, forming a third trench below the second trench by a second etching process using the insulating spacers as etch masks, and removing the insulating spacers above the third trench. In addition, the method includes forming a first isolation structure in the first trench and a second isolation structure in the second trench and the third trench.

The fins described above may be patterned by any suitable method. For example, the fins may be patterned using one or more photolithography processes, including double-patterning or multi-patterning processes. Generally, double-patterning or multi-patterning processes combine photolithography and self-aligned processes, allowing patterns to be created that have, for example, pitches smaller than what is otherwise obtainable using a single, direct photolithography process. For example, in one embodiment, a sacrificial layer is formed over a substrate and patterned using a photolithography process. Spacers are formed alongside the patterned sacrificial layer using a self-aligned process. The sacrificial layer is then removed, and the remaining spacers may then be used to pattern the fins.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for forming a semiconductor device structure, comprising: forming a first well region and a second well region in a semiconductor substrate, wherein the first well region and the second well region have different conductivity types, and a well interface is formed between the first well region and the second well region; patterning the semiconductor substrate to form a first fin structure in the first well region, a second fin structure in the second well region, and a first trench between the first fin structure and the second fin structure, wherein the first trench exposes the well interface in the semiconductor substrate; forming insulating spacers on opposite sidewalls of the first trench; etching the semiconductor substrate below the first trench using the insulating spacers as an etch mask, to form a second trench below the first trench; and filling the first trench and the second trench with an insulating material.
 2. The method as claimed in claim 1, wherein the semiconductor substrate is etched by an anisotropic etching process, and wherein the second trench has tilted sidewalls.
 3. The method as claimed in claim 1, wherein the semiconductor substrate is etched by an isotropic etching process, and wherein the second trench has a convex surface.
 4. The method as claimed in claim 1, wherein during patterning of the semiconductor substrate, a third fin structure is formed in the first well region, a fourth fin structure is formed in the second well region, a third trench is formed between the first fin structure and the third fin structure, and a fourth trench is formed between the second fin structure and the further fin structure; and wherein the insulating material is filled into the third trench and the fourth trench.
 5. The method as claimed in claim 4, wherein the insulating material in the third trench and the fourth trench is entirely covered by the bottom surfaces of the third trench and the fourth trench.
 6. The method as claimed in claim 1, further comprising: recessing the insulating material, so as to form an isolation structure in the first trench and the second trench; and forming a gate structure over the first fin structure and the second fin structure, wherein the gate structure comprises: a gate dielectric layer; and a gate electrode layer over the gate dielectric layer.
 7. The method as claimed in claim 1, further comprising: removing the insulating spacers before filling the first trench and the second trench with the insulating material.
 8. The method as claimed in claim 1, wherein the insulating material in the first trench has a top surface that is substantially level with a top surface of the first well region and a top surface of the second well region.
 9. The method as claimed in claim 1, wherein the second trench is directly above the well interface.
 10. A method for forming a semiconductor device structure, comprising: forming an undoped region, a first well region, and a second well region in a semiconductor substrate, wherein the first well region and the second well region are below the undoped region and adjacent to each other; patterning the doping region, the first well region and the second well region to form a plurality of fin structures protruding from the semiconductor substrate; forming two insulating spacers on two opposite sidewalls of each of the plurality of fin structures, wherein the insulating spacers expose a portion of the first well region and a portion of the second well region; etching the exposed portion of the first well region and the exposed portion of the second well region to form a plurality of trenches in the semiconductor substrate; removing the insulating spacers above the plurality of trenches; and correspondingly forming a plurality of isolation features in the plurality of trenches after the removal of the insulating spacers.
 11. The method as claimed in claim 10, wherein each of the plurality of isolation features comprises: a first isolation portion formed between adjacent two of the plurality of fin structures; and a second isolation portion extends from a bottom surface of the first isolation portion, wherein a top surface of the first isolation portion is substantially level with an interface between the undoped region and the first well region and an interface between the undoped region and the second well region.
 12. The method as claimed in claim 11, wherein the first isolation portion has a bottom width that is greater than a top width of the second isolation portion.
 13. The method as claimed in claim 10, wherein the exposed portion of the first well region and the exposed portion of the second well region are etched by an anisotropic etching process, and wherein each of plurality of trenches has tilted sidewalls.
 14. The method as claimed in claim 10, wherein the exposed portion of the first well region and the exposed portion of the second well region are etched by an isotropic etching process, and wherein each of plurality of trenches has convex sidewalls.
 15. The method as claimed in claim 10, further comprising: forming a gate structure over each of the plurality of fin structures.
 16. A method for forming a semiconductor device structure, comprising: forming a first well region and a second well region in a semiconductor substrate, wherein a well interface is formed between the first well region and the second well region; forming a first fin structure in the first well region, a second fin structure in the second well region, and a third fin structure in the first well region and between the first fin structure and the second fin structure by a first etching process, so that a first trench is formed between the first fin structure and the third fin structure and a second trench is formed between the third fin structure and the second fin structure, wherein the second trench is directly above the well interface; forming insulating spacers on opposite sidewalls of the second trench; forming a third trench below the second trench by a second etching process using the insulating spacers as etch masks; removing the insulating spacers above the third trench; and forming a first isolation structure in the first trench and a second isolation structure in the second trench and the third trench.
 17. The method as claimed in claim 16, wherein the second etching process is an anisotropic etching process, and wherein the third trench has tilted sidewalls.
 18. The method as claimed in claim 16, wherein the second etching process is an isotropic etching process, and wherein the third trench has convex sidewalls.
 19. The method as claimed in claim 16, further comprising: forming a gate structure over the first fin structure, the second fin structure, and the third fin structure.
 20. The method as claimed in claim 16, wherein each of the first fin structure, the second fin structure, and the third fin structure comprises an undoped region, and wherein a bottom surface of the undoped region is substantially level with a top surface of the first isolation structure and a top surface of the second isolation structure. 